An earphone or ear bud is a small device inserted into the ear and converts an electric signal into a sound signal. It can be used to hear sounds alone using a portable radio set, a hearing aid, or a music listening device.
However, earphones in the current market only allow sounds to be heard in one direction. These headphones do not use bone conduction and air conduction together, and are not comfortable when inserted into the ear hole of the user.
Meanwhile, a person can listen to sounds using two types of principles, air conduction and bone conduction. Air conduction is a principle in which sounds transfer to the inner ear through the eardrum via air media. Bone conduction transfers sounds to the cochlea through the cranial bone and reaches the brain via acoustic nerves.
Bone conduction is based on the principle that sounds are heard through the vibration of the cranial bone of the user. A bone conduction transducer has been developed on the principle of bone conduction.
The bone conduction transducer is a transducer that converts an electric signal into a vibration signal. Using the principle of bone conduction, the position where a user can hear the optimal sounds is as follows. Accordingly, bone conductive headsets and headphones have been invented.
If a bone conduction headset or headphone is used, the auditory sense of a user is never damaged even when used for long periods of time. However, existing air conduction headsets can show its original function only when it is accurately attached to an ear of a user. Moreover, when it is used for high frequency sounds for a long time, the auditory sensor of the user can be seriously damaged.
On the other hand, since a bone conduction headset or headphone enables hearing of sounds through vibration of the cranial bone of a user, the auditory sense of the user is never damaged even when used for long periods of time. Moreover, since the bone conduction headset does not cover the ear of the user, it is also more comfortable to wear.
Various applied products may result in more convenience in the lives of users. That is, the application areas may been widened to application fields such as tactical products as well as communication devices for aurally handicapped persons, multi-media appliance products, and products for VoIPs, mobile phones, and telephones.
Moreover, a user can perform clear transmission and reception through the headsets even in noisy environments more than 90 dB. When carrying the headset as earplugs, noise sensitivity is reduced by more than 20 dB, and exact reception sensitivity may be obtained even in noisy environments.
The foregoing bone conduction technology is very valuable, and was suggested in the invention of a previous application of the applicant.
Namely, referring to FIGS. 1(a) and 1(b), a speaker using bone conduction is disclosed in Korean Patent Application No. 2008-0028583.
In the shock absorbing unit of the patent application, an upper case 101 and a lower case 106 are engaged with upper and lower ends of a shaft 103, respectively. A vibrating plate 104, a weighting plate 102, a yoke 105, a magnet 112, and an inner plate 109 are connected to the outer peripheral surface of the shaft housing 108 into which the shaft 103 is inserted. A filler 113, i.e. silicone is filled in an aperture between the shaft 103 and the shaft housing 108. Second and first shaft engaging holes 101a and 106a are respectively formed in the upper and lower cases 101 and 106, and upper and lower ends of the shaft 103 are inserted into the second and first engaging holes 101a and 106a respectively. Fifth, fourth, third, second, and first shaft housing engaging holes 104a, 102a, 105a, 112a, and 109a are respectively formed in the vibrating plate 104, the weighting plate 102, the yoke 105, the magnet 112, and the inner plate 109 inserted into the outer peripheral surface of the shaft housing 108. A coating layer preventing penetration of water and foreign substances is provided in a region where the shaft 103 and the upper and lower cases 101 and 106 are engaged with each other. A frequency range controller 100a constitutes a magnetic field circuit that provides a robust vibrating force in a frequency band ranging 100 to 250 Hz according to the weight alteration of the weighting plate 102. Reference numeral 107 represents a printed circuit board (PCB).
Existing bone conduction speakers may be resistant to a strong shock and show a robust vibrating force. However, in this bone conduction speaker a chamber is not formed at the outer corner of the yoke 105, so a spring touch cannot be prevented during a bass sound.
In the existing bone conduction speaker, since the shaft 103 and the lower case 106 are not formed integrally, if a shock occurs, centering is not maintained so that it cannot act as a vibrator.
Moreover, since the existing bone conduction speaker does not include a piezoelectric element, it cannot play back high frequency sounds.